The formation, ultrastructure and biochemistry of actin-containing filaments and filament bundles will be investigated in a model system, i.e., echinoderm coelomocytes. On class of coelomocytes, the leukocytes, undergoes a remarkable transformation from a petaloid to a filopodial form. The control of this transformation, involvinga reorganization of actin-containing filaments into filament bundles, will be investigated with light and electron microscopy, including in situ S-1 binding. The isolation of filament bundles will allow optical diffraction comparisons with other actin paracrystalline structures, analysis for accessory proteins with SDS-gel electrophoresis, reactivation and template growth studies. The ability of the actin-containing filaments to enhance myosin ATPase will be determined and related to the presence or absence of actin binding proteins or other regulatory factors. Comparative studies of muscle, egg and coelomocyte actin will be accomplished with tryptic peptide mapping. Also, comparisons of actomyosin and control proteins in an amoeboid cell type will be included and related to its different motile activities. In addition, the proprties and release of gel-forming proteins, which aid in clot formation of these coelomocytes, will be analyzed.